A robust assay for dexamethasone in plasma using a heterologous 125I radioligand and a magnetizable solid-phase antiserum.
An assay using an antiserum raised against a dexamethasone 21-hemisuccinate conjugate and the heterologous radioligand dexamethasone 21-(carboxymethyl) ether was developed, validated, and used to study the pharmacokinetics of this steroid for 12 h following administration to patients with congenital adrenal hyperplasia. Coupling the antiserum to magnetizable cellulose allowed rapid separation of bound/free steroid. A C-21 rather than a C-3 antiserum was used to minimize interference with a main metabolite, 6 beta-hydroxydexamethasone. Close correspondence of assay (0.35 nmol/L) and curve (0.25 nmol/L) sensitivities suggests that interference by matrix effects is minimal. This was confirmed by good agreement in data from the in-house assay and that of a reference procedure. Good precision was demonstrated by the precision profile and Shewhart chart quality control data. The latter also demonstrated the assay was robust and reliable in routine practice.
Cook
N J
NJ
Tenovus Institute for Cancer Research, University of Wales College of Medicine, Heath Park, Cardiff, UK.
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G F
GF
Lejeune-Lenain
C
C
Riad-Fahmy
D
D
D000293:Adolescent; D000312:Adrenal Hyperplasia, Congenital / Q000097:blood*; D000328:Adult; D003907:Dexamethasone / Q000097:blood* / Q000493:pharmacokinetics; D006801:Humans; D007106:Immune Sera; D007457:Iodine Radioisotopes; D008280:Magnetics; D011863:Radioimmunoassay; D011869:Radioligand Assay
D007106:Immune Sera; D007457:Iodine Radioisotopes; D003907:Dexamethasone